NEWS: mention Array#append and Array#prepend

[Feature #12746] [ci skip]

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@58257 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

NEWS

@@ -20,6 +20,11 @@ with all sufficient information, see the ChangeLog file or Redmine
 
 === Core classes updates (outstanding ones only)
 
+* Array
+
+  * Array#append  [Feature #12746]
+  * Array#prepend  [Feature #12746]
+
 * Integer
 
   * Integer.sqrt  [Feature #13219]